This invention is the result of many years spent studying the effects of kite-construction factors, and eliminating those considered to be detrimental to balanced flight. These are.
1. Central stiffening member; As the kite rides the wind it tries to follow the shape of the laminar. A central member causes strain and drag.
2. Non-rigid leading edge to ventral fin: As wind hits the kite from the side, these fins distort and throw the kite off course by presenting a curved edge to the oncoming laminar.
3. Central support for cross-stay: This was found to take a great strain where it crosses the mast, and was discarded in favour of a cross-stay on the back of the kite.
4. Vee-shaped bridles: These tend to hold the kite too much on the wind. A single fulcrum flies the kite higher above the flier and adjusts to gusts.
A study of hang-gliders led to the attempt to fly a model as a kite. This performed well in moderate air, but badly in gusts. By sewing together the wings in a straight line (see Bochau U.S. Pat. No. 1,105,058) the kite, being three-dimensional, was found to ride in almost any air, but sailed too quickly through the wind on ocean beaches. By using the shape of the veins on a butterfly's wing painted on to the kite as the top of the keel, it was found that sufficient drag was obtained to allow the kite to fly in high wind. It was also found that side gusts could be used for lift, and that the kite would flap it's wings if left tethered, and that the wings could be made to flap by pulling with a pumping action on the line. In a free fall, this kite ravels further on a reach than either into or with the wind. There is relatively little strain on any member as the fabric adjusts to the wind, straightening the curve when necessary.
The object of this invention is to make a safe, stable kite that will fly in heavy or light winds, as a hand kite tethered to a line.
Previous delta wing kites developed from the Rogallo kite are unstable in high winds and prone to stress. Such kites usually have a bridle or ventral fin of fabric below the keel, for the line, and too much tension on the line causes the kite to become distorted and dive. Box-kites, being fixed in three dimensions, are stable in high winds.
This trefoil kite combines the great sail area of the delta wing kite with the stability of the box-kite, by joining the two sails together, almost parallell to and a short distance from, the mast, forming three foils -- two horizontal wings and one vertical keel.
This device was found to set the two sails, one against the other, in a good flying shape. The mast, being the lowest part of the kite, cuts the wind and flows it squarely up to the sails.
When the vertical keel area of sail has an aerodynamic curve where the keel foil joins the wing foils, the contour adapts to the wind velocity and compensates for bending of the mast, resulting in a very stable kite. The joining by stitching together the two sails some distance from the mast is the preferred part of the design, because it combines the flat kite and the box-kite in a soft flexible shape, using only a mast, two spars and a cross-stay as support.